Boltzmann expansion in a radiofrequency conical helicon thruster operating in xenon and argon

A low pressure (similar to 0.5mTorr in xenon and similar to 1mTorr in argon) Boltzmann expansion is experimentally observed on axis within a magnetized (60 to 180 G) radiofrequency (13.56 MHz) conical helicon thruster for input powers up to 900 W using plasma parameters measured with a Langmuir probe. The axial forces, respectively, resulting from the electron and magnetic field pressures are directly measured using a thrust balance for constant maximum plasma pressure and show a higher fuel efficiency for argon compared to xenon. (C) 2013 AIP Publishing LLC.